In the production of glass filaments, it is conventional to flow streams of molten glass from closely spaced orifices in the bottom or discharge wall of an electrically heated, precious metal alloy feeder or bushing.
For the production of continuous glass filaments, there are two general types of feeders available. The more widely used type employs a bottom wall having stream defining orifices provided in projections or tips, depending from the exterior surface of the bottom wall. The second, a more recently developed type, employs an orificed bottom wall having a plainer exterior surface. The first type is known as a "tipped" feeder; for example, see U.S. Pat. Nos. 4,222,757 and 4,321,074. The second type of feeder is known as a "tipless" feeder; for example, see U.S. Pat. No. 3,905,790.
Historically, glass fiber forming operations have been plagued by primarily two phenomena occurring after a filament break--flooding and bead drops.
Recently, a glass fiber forming system has been developed that dramatically reduces the effects of disruptive filament breaks. U.S. Pat. No. 4,488,891, issued to Grubka et al, discloses a fiber forming system otherwise known as "dripless". That is, during operation if a filament breaks, the glass will cease to flow from the orifice associated with the break while attenuation is maintained from the remaining orifices. Thus, the glass does not drip from the orifice of the reversed filament.
The advantages of such a system are clear. Some of the disadvantages include (1) utilization of higher amounts of alloy and fabricating such feeders; and (2) increased "restart" times, as compared to conventional feeders, when the number of filament breaks ultimately requires the restart of the attenuation process at the disrupted orifices. Since the diameter of the dripless orifice is generally larger than the diameter of the non-dripless orifice, to produce the same diameter fiber, fewer orifices can be located in a given area. Thus, the size of the feeder discharge wall, among other things, must be larger to accommodate an equal number of filament producing orifices.